The invention relates to a method and apparatus for milking mammals, including cows.
Milking systems withdraw milk from the milk secreting glands of mammals by applying negative pressure (pressure below atmospheric pressure), i.e. vacuum, to the teat. A plurality of teat cups are provided, each having a liner, or inflation, around a respective teat, lo and defining a milk flow passage within the liner below the teat, and a pulsation chamber outside the liner between the liner and the teat cup. The milk flow passage within the liner supplies milk to a milking claw which also receives milk from the milk flow passages of the other liners of the other teat cups.
Simply supplying a constant vacuum to the teat is not desirable because it causes the tissue of the teat to become engorged with blood and lymph. When these fluids are confined to their normal spaces within the teat, the condition is called congestion. When the fluids leave their normal spaces, it is called oedema. These conditions may result in pain or discomfort to the mammal being milked, and swelling of the tissue which may constrict the duct through which milk is being withdrawn, thereby slowing the flow of milk. The slowing of milk flow due to the effects of congestion may be accompanied by a reduced volume of milk available for removal because the discomfort may interfere with the milk ejection reflex by which the mammal presents her milk to the teat.
Various attempts have been made to ameliorate the undesirable effects of vacuum on the teat by carefully shaping the teat cup and liner to support the teat as well as possible, and by periodically relieving the vacuum to the teat. The liner periodically collapses around and below the teat, providing massage to the teat. The massage compresses the end of the teat, thereby actively forcing fluids out of the teat apex. The massaging action of the liner also provides stimulation to the teat whereby the milk ejection reflex is strengthened. In some cases, the milk ejection reflex may be elicited solely by the action of the pulsating liner. The pulsation cycle has an on portion and an off portion. Milk is withdrawn from the teat through the liner to the claw during the on portion. During the off portion, the closed liner stops milk flow from the teat.
In the prior art, a two-way valve, or pulsator, alternates between a first condition connecting a negative pressure source, i.e. vacuum, to the pulsation chamber, and a second condition supplying atmospheric or higher pressure to the pulsation chamber. The two-way valve provides a pulsation cycle having an on portion during the first condition of the valve, and an off portion during the second condition of the valve. The valve or pulsator simply transfers the pulsation chamber connection between two alternative sources, namely vacuum and atmosphere.
In the prior art, it is known to replace the atmospheric pressure source with a source above atmospheric pressure for some part of the milking (positive pressure pulsation). It is also known to use a vacuum level other than milking vacuum to replace the vacuum source. It is also known to vary the repetition rate or ratio between atmospheric and vacuum phases of pulsation. These changes may be varied during milking, either on a fixed program or under the control of the flow of milk from the mammal. The rate of transition from atmospheric to vacuum may be changed by selecting the sizes of orifices used in the pulsator. However, the pulsator remains a two-way valve.